Picornaviruses affect their host cells by synthesizing virus specific proteins and by recruiting host proteins for use during viral replication and expression. We have demonstrated that conserved RNA sequences occur at the 5' end of three divergent enterovirus genomes: poliovirus type 1, poliovirus type 2 and coxsackie virus B1. Conserved sequences within these enterovirus genomes may function as specific regulatory sites. The complete structure of the 5' region of these genomes will be determined, including the ribosome binding site and the initiation sequence for the first viral gene product. Sequencing will be aided by the construction of a set of recombinant DNA molecules representing various regions of the poliovirus genome. The location and extent of homologous regions within enterovirus genomes will be mapped by RNA:RNA and RNA:DNA heteroduplex analysis. Host or viral proteins which bind specifically to 5' or 3' conserved sequences will be identified as possible regulatory factors. Compounds which inhibit this specific binding will be tested for their effect on the course of virus infection in HeLa cells. Temperature sensitive mutants, such as tsB9, will be examined to determine the nature of their genetic defect. The mutant tsB9 is defective in both RNA synthesis and in the assembly of procapsid. The relationship between viral assembly and RNA replication will be explored with this mutant. The data from the proposed sets of experiments will be used to define strategic events during the virus life cycle which involve interactions with host functions. Since these viruses cause a series of disease states, from mild enteric infections to severe neurological disorders, we must understand aspects of their molecular pathology at the cellular level.